Quantifying vegetation areas according to urban gradient: an analytic framework for urban ecology studies.
Abstract
In a context of growing urbanization, it appears that the conservation of natural/seminatural urban greenspaces may help to limit the erosion of biodiversity and to maintain ecological functions that are beneficial to humans. Therefore, the urban complex has become a research topic in ecology, with the underlying objective of understanding links between the spatial structure of cities and the biological processes that occur within them. The urban gradient approach can improve our understanding of these relationships. Initially, the estimation of human influence was limited to descriptions of land use, along transects, using density calculations (of population, buildings or roads). More recently, new methods have been developed to better quantify urban gradient characteristics, taking into account matrix complexity, establishing new land use and land cover classifications more appropriate for urban ecology issues, or through the selection of relevant indicators (partly inspired by landscape ecology). The calculation of quantitative descriptors raises methodological challenges such as: availability, heterogeneity, quality and processing of data; choice of appropriate indicators and linking spatial scales. This communication proposes an approach for quantifying urban gradient characteristics via an analytical framework for urban areas, applied at different spatial scales (field, urban block, district, urban area). This method, supported by GIS and remote sensing, is meant to be integrative (multisource data from national databases, production of additional data from satellite imagery), accessible (technically and financially), and suitable for urban ecology questions (vegetation mapping, plant and animal distribution analysis, urban climatology, landscape planning). Three cities of western France are studied (La Roche-sur-Yon, Angers, Nantes), ranging from medium sized to large urban areas. The method provides ecologists with a description of the urban complex, allowing a better description of the context of study sites, descriptive indicators for improving sampling strategy and a series of explanatory variables to test the response of living organisms to urbanization. Finally, the objective will be to identify districts with high ecological potential.